.div1{
    width: 0px;
    height: 0px;
    border:125px solid transparent;
    border-bottom-color: yellow;
    display: inline-block;
}

.div2{
    width: 0;
    height: 0;
    border: 125px solid transparent;
    border-top-color: yellow;
   display: inline-block;
}

.div3{
    width: 0;
    height: 0;
    border: 125px solid transparent;
    border-left-color: yellow;
    display: inline-block;
}

.div4{
    width: 0;
    height: 0;
    border: 125px solid transparent;
    border-right-color: yellow;
    display: inline-block;
}


/*什么都没有，单单设置底部边框，边框宽高跟内容的一样也为0了*/
.div5{
    width: 0;
    height: 0;
    border-bottom: 250px solid #ed1250;
    display: inline-block;
}
